Ophthalmic lenses, in particular contact lenses, which it is intended to produce economically in large numbers, are preferably produced by the so-called mold or full-mold process. In order to produce a contact lens, usually a specific amount of a flowable lens forming material is introduced into the female mold half in a first step. The mold is then closed by putting the male mold half into place. The subsequent polymerization and/or cross-linking of the lens forming material is carried out by means of irradiation with UV light and/or by heating. After the lens if formed, the mold is disassembled and the lens removed. Additional processing steps, such as inspection, extraction, hydration, surface treatment and sterilization may finally be performed on the lens before packaging.
For cosmetic purposes, contact lenses having one or more colorants printed on the lens or onto the molds that are then used to make the contact lenses are in high demand. These colored contact lenses may enhance the natural beauty of the eye and/or may provide unique patterns on the iris of the wearer. Further, non cosmetic patterns or marks, such as rotation marks, inversion marks, product codes and/or lot numbers may be printed onto the contact lenses or onto the molds that are then used to make the contact lenses. Said non cosmetic patterns or marks are of particular benefits to wearers, eye-care practitioners and manufacturers.
Various methods have been disclosed for printing either directly onto the contact lenses or onto the molds that are then used to make the contact lenses.
A printing fluid, i.e. an ink, can be applied to a contact lens or to a mold according to known printing technologies, such as, for example ink jet printing.
Typical inks for ink jet applications, have one or more of the following characteristics: a viscosity lower than 50 m Pa·s, preferably lower than 15 m Pa·s; most preferably below 15 m Pa·s; a surface tension of from 20 mN/m to 60 mN/m; a particle size of less than 5 μm, preferably lower than 1 μm; most preferably below 0.5 μm; prolonged stability (i.e., stable for at least 4 hours, preferably at least 8 hours, more preferably at least 24 hours); an appropriate color level (visible by eye); uniform drop formation and jet stability; good adhesion to contact lenses; good transfer from a mold to a contact lens made in the mold.
A common problem in ink jet printing is the clogging of the nozzles in the print head due to bubbles or contaminants in the ink channels or due to increase in ink viscosity.
WO-A-2006/116415 discloses a print head maintenance station for an industrial printing apparatus which is used to prevent clogging of the print head, particularly during periods in which the print head is idle. The maintenance station includes a capping station which has sockets for keeping the print head moist, and a blotting station for cleaning any residual printing fluids prior to carrying out a print function.
In the manufacture of contact lenses, which are intended to be produced economically in large numbers, fast drying inks and/or UV curable inks are used, as for example described in WO-A-2003/040242. In particular with said fast drying and/or UV curable inks, fully or partly cured and/or fully or partly dried ink adhering to the ink nozzles can lead to persistent clogging of the same.
It has now been found, that conventional maintenance stations, as for example described in WO-A-2006/116415, are not suitable for fast drying inks and/or UV curable inks as used in the manufacture of contact lenses, in particular in the manufacture of silicone hydrogel contact lenses, which are provided with a printed image thereon.
Accordingly, it is an object of the present invention to provide an improved apparatus for cleaning a print head, in particular an ink jet print head, from adhered ink which is fully or partly cured and/or fully or partly dried.
It is a further object of the present invention to provide an improved apparatus for maintaining a print head, in particular an ink jet print head, sufficiently wet during periods in which the print head is idle.
It is still a further object of the present invention to provide an apparatus useful for the manufacture of a contact lens, in particular a silicone hydrogel contact lens, which is provided with a printed image thereon.